The invention relates to the preparation of ceramic precursor compositions, and more particularly to the preparation of ceramic metal oxide-containing powders.
A common method for the production of sub-micron sized powders of ceramic precursor compositions is precipitation or co-precipitation of an oxide precursor from aqueous solution of a salt of the metal or metals to be used. Commonly, oxides, hydroxides, oxycarbonates, oxalates, etc. all usually with varying degrees of hydration, are precipitated at an appropriate pH. In such cases, the precipitate frequently has inhomogeneities due to variations within the reaction vessel or forms a gel. Both of these present practical processing problems. For instance, filtration of the gel is often difficult because of clogging of the pores of the filter, desalting of the gel by washing is tedious, and oven drying of a purified gel often yields unsinterable powders. Inhomogeneities result in low green densities and poor sintering behavior.
Other established methods for the production of sinterable ceramic precursor compositions include high temperature oxidation of metal salts with oxygen and/or water vapor, hydrolysis and thermal decomposition of alkoxides and hydrothermal reaction of metals or alloys. Such methods usually require complex and expensive equipment and/or expensive starting materials and thus find relatively little industrial use.
It is desirable that sub-micron sized powders of the ceramic precursor compositions prepared by such methods be highly reactive, sinter at relatively low temperatures, provide relatively high green (presintered) densities, be amenable to film-forming techniques such as tape casting and give finished ceramic compositions with desirable microstructures.
Accordingly, it an object of the present invention to provide a novel method for preparing ceramic precursor compositions by controlling the microstructure of such compositions.